Method for making conductive polymer, and composite film and circuit board having the conductive polymer

ABSTRACT

A method for making a conductive polymer for electromagnetic shielding purposes includes steps of mixing liquid crystal monomers, a silver complex, an initiator, and a catalytic agent in certain proportions by weight to form a mixture. A solvent is added into the mixture, the mixture and the solvent being in a ratio from 3:17 to 1:3 by weight. The mixture is heated to undergo an atom transfer radical polymerization.

FIELD

The subject matter herein generally relates to a method for making aconductive polymer, and a composite film and a circuit board having theconductive polymer.

BACKGROUND

Circuit boards usually include electromagnetic shielding layers made ofconductive or magnetic materials for blocking electromagnetic signals.One electromagnetic shielding layer may include an adhesive layer, acopper layer, and a solder mask layer. However, it is hard toelectrically connect the copper layer to the solder mask layer using achemical plating or electroplating process, and the copper layerconnected thereto is easily peelable.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures.

FIG. 1 is a diagrammatic view of an exemplary embodiment of a compositefilm according to the present disclosure.

FIG. 2 is a diagrammatic view showing through holes defined in thecomposite film of FIG. 1.

FIG. 3 is a diagrammatic view of a flexible board to support thecomposite film of FIG. 1.

FIG. 4 is a diagrammatic view showing the flexible board of FIG. 3 beingattached to the composite film of FIG. 2.

FIG. 5 is a diagrammatic view showing a copper layer formed on thecomposite film of FIG. 4.

FIG. 6 is a diagrammatic view showing a solder mask layer formed on thecopper layer of FIG. 5.

FIG. 7a is an eye pattern of a signal waveform from a circuit board ofone exemplary embodiment, transmitting signals at 5 Gbps.

FIG. 7b is similar to FIG. 7a , but showing the circuit boardtransmitting signals at 10 Gbps.

FIG. 8a is an eye pattern of a signal waveform from a circuit board ofone comparative exemplary embodiment, transmitting signals at 5 Gbps.

FIG. 8b is similar to FIG. 8a , but showing the circuit boardtransmitting signals at 10 Gbps.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the exemplary embodiments described herein.However, it will be understood by those of ordinary skill in the artthat the exemplary embodiments described herein can be practiced withoutthese specific details. In other instances, methods, procedures, andcomponents have not been described in detail so as not to obscure therelated relevant feature being described. Also, the description is notto be considered as limiting the scope of the exemplary embodimentsdescribed herein. The drawings are not necessarily to scale and theproportions of certain parts may be exaggerated to better illustratedetails and features of the present disclosure.

The term “comprising,” when utilized, means “including, but notnecessarily limited to”; it specifically indicates open-ended inclusionor membership in the so-described combination, group, series, and thelike.

An exemplary embodiment of a conductive polymer which can be used in acircuit board is described. The conductive polymer is made by heating amixture comprising liquid crystal monomers, a silver complex, aninitiator, and a catalytic agent, and a solvent, to cause the mixture toundergo an atom transfer radical polymerization (ATRP). The liquidcrystal monomers have a mass percentage of about 42.2% to about 52.2% ofa total mass of the mixture. The silver complex has a mass percentage ofabout 43.1% to about 53.1% of the total mass of the mixture. Theinitiator has a mass percentage of about 0.85% to about 1.35% of thetotal mass of the mixture. The catalytic agent has a mass percentage ofabout 2.85% to about 4.35% of the total mass of the mixture. The mixtureand the solvent are in a ratio from 3:17 to 1:3 by weight. After theatom transfer radical polymerization, the silver complex is wrapped inthe conductive polymer which causes the conductive polymer to beelectrically conductive.

The liquid crystal monomers are selected from a group consisting of2,5-bis[(4methoxyphenyl)oxycarbonyl]styrene

4-vinyl benzene and derivant thereof

R can be H, Me, t-Bu, Br, F, CF₃, or OAc), methyl acrylate

hydroxyethyl acrylate

vinyl acrylate

N,N-dimethylamino propenyl ketone

acrylonitrile

methyl methacrylate

butyl methacrylate

N,N-dimethylaminoethyl methacrylate

and tert-butyl methacrylate

In at least one exemplary embodiment, the liquid crystal monomers are2,5-bis[(4methoxyphenyl)oxycarbonyl]styrene which can cause theconductive polymer to form side chains for wrapping the silver complexin the conductive polymer.

The silver complex can be selected from a group consisting of silvernitrate (AgNO₃), silver oxide (Ag₂O), AgBP₄, and AgPF₆. In at least oneexemplary embodiment, the silver complex is silver nitrate.

The initiator can be selected from a group consisting of1,3,5-(2′-bromo-2-methylpropionato)benzene

α-bromine ethane

2-ethyl bromide

2-bromine-2-methyl ethyl propionate

and 2-dibromine propionitrile

In other exemplary embodiments, the initiator can be other halides suchas other alkyl halides, benzyl halides, α-bromine compounds,α-haloketones, α-halogen halides, aryl sulfonyl chloride, orazobisisobutyronitrile. In at least one exemplary embodiment, theinitiator is 1,3,5-(2′-bromo-2-methylpropionato)benzene which can causethe conductive polymer to form side chains for wrapping the silvercomplex in the conductive polymer.

The catalytic agent can be copper bromide (CuBr). In other exemplaryembodiments, the catalytic agent can be copper bromide and sparteine.

The solvent can be selected from a group consisting of dimethylsulfoxide (DMSO), dimethylformamide (DMF), and N-methyl-2-pyrrolidone(NMP). In at least one exemplary embodiment, the solvent isN-methyl-2-pyrrolidone.

An exemplary embodiment of a method for making the conductive polymercomprises the following steps. The liquid crystal monomers, the silvercomplex, the initiator, and the catalytic agent are mixed to form amixture. The solvent is added into the mixture, and the mixture isheated to undergo atom transfer radical polymerization.

FIG. 1 illustrates a composite film 10 comprising a base layer 11 madeof liquid crystal polymer and a conductive layer 13. The base layer 11comprises an active surface 111 treated by plasma activation. Theconductive layer 13 is formed on the active surface 111 by coating theconductive polymer on the active surface 111. This causes the silvercomplex in the conductive polymer to be bonded to the active surface111.

The composite film 10 can further comprise an adhesive layer 15 incontact with a surface of the base layer 11, which is opposite to theactive surface 111.

Referring to FIGS. 1-6, each step of a method for making a circuit board100 is presented in accordance with an exemplary embodiment. Theexemplary method for making the circuit board 100 is provided by way ofexample, as there are a variety of ways to carry out the method. Theexemplary method can begin at step 1.

At step 1, referring to FIG. 1, at least one composite film 10 isprovided, which comprises the base layer 11 comprising the activesurface 111, the conductive layer 13 formed on the active surface 111,and the adhesive layer 15 formed on the surface of the base layer 11which is opposite to the active surface 111.

At step 2, referring to FIG. 2, at least one through hole 101 is definedin the composite film 10 which goes through the adhesive layer 15, thebase layer 11, and the conductive layer 13. In at least one exemplaryembodiment, the through hole 101 is defined by punching or etching.

At step 3, referring to FIG. 3, a flexible board 20 is provided, whichcomprises a substrate 21 and at least one conductive wiring layer 23formed on one surface of the substrate 21. The flexible board 20 can bea single-sided board, a double-sided board, or a multiple-sided board.In at least one embodiment, the flexible board 20 is a double-sidedboard which comprises two conductive wiring layers 23 formed on oppositesurfaces of the substrate 21.

At step 4, referring to FIG. 4, the composite film 10 is attached to theflexible board 20 to cause at least one conductive wiring layer 23 to beformed on the adhesive layer 15.

At step 5, referring to FIG. 5, a copper layer 30 is formed on theconductive layer 13 to cause the copper layer 30 to further cover aninner wall of the through hole 101. Thereby, the conductive layer 13 iselectrically connected to the conductive wiring layer 23 by the throughhole 101. In at least one exemplary embodiment, the copper layer 30 canbe formed by electroplating or chemical plating.

At step 6, referring to FIG. 6, a solder mask layer 40 is formed on thecopper layer 30 to cause the solder mask layer 40 to further cover theinner wall and a bottom surface of the through hole 101.

FIG. 6 illustrates that the circuit board 100 comprises a flexible board20, a composite film 10 formed on the flexible board 20, and a copperlayer 30 formed on the composite film 10. The composite film 10comprises the base layer 11 having the active surface 111, theconductive layer 13 formed on the active surface 111, and the adhesivelayer 15 formed on the surface of the base layer 11 opposite to theactive surface 111. The composite film 10 is formed on the flexibleboard 20 by the adhesive layer 15. The composite film 10 defines the atleast one through hole 101 which goes through the adhesive layer 15, thebase layer 11, and the conductive layer 13. The copper layer 30 coversthe conductive layer 13 and the inner wall of the through hole 101, andis electrically connected to the flexible substrate 20 by the throughhole 101.

In at least one exemplary embodiment, the flexible board 20 is adouble-sided board which comprises the substrate 21 and two conductivewiring layers 23 formed on opposite surfaces of the substrate 21.

In at least one exemplary embodiment, the circuit board 100 furthercomprises the solder mask layer 40. The solder mask layer 40 covers thecopper layer 30, the inner wall and the bottom surface of the throughhole 101.

EXAMPLE

2,5-bis[(4methoxyphenyl)oxycarbonyl]styrene of 105.9 g, AgNO₃ of 108 g,1,3,5-(2′-bromo-2-methylpropionato)benzene of 2.5 g, CuBr of 1.9 g, andsparteine of 6.1 g were mixed to form a mixture. 864 g of NMP was addedinto the mixture and heated under 90 □ to form a conductive polymer. Acomposite film 10 was made by using the conductive polymer. A circuitboard 100 was made by using a flexible board 20, the composite film 10,a copper layer 30, and a solder mask layer 40.

COMPARATIVE EXAMPLE

A circuit board was made by using a flexible board 20 and a conventionalelectromagnetic shielding layer. The electromagnetic shielding layercomprises an adhesive layer, a copper layer 30, and a solder mask layer40. The adhesive layer has a thickness equaling that of the compositefilm 10 of the above example.

The signal waveforms from the circuit board 100 of the example above fortransmitting signals at 5 Gbps and 10 Gbps were tested to obtain the eyepatterns shown in FIGS. 7a and 7b . The signal waveforms from thecircuit board of the above comparative example for transmitting signalsat 5 Gbps and 10 Gbps were also tested to obtain the eye patterns shownin FIGS. 8a and 8b . Comparing the circuit board of the examples, thecircuit board 100 of the example above has an improved ability forblocking electromagnetic signals according to a comparison between eyeheights and eye widths in the eye patterns.

It is to be understood, even though information and advantages of thepresent embodiments have been set forth in the foregoing description,together with details of the structures and functions of the presentembodiments, the disclosure is illustrative only; changes may be made indetail, especially in matters of shape, size, and arrangement of partswithin the principles of the present embodiments to the full extentindicated by the plain meaning of the terms in which the appended claimsare expressed.

What is claimed is:
 1. A method for making a conductive polymercomprising: mixing liquid crystal monomers, a silver complex, aninitiator, and a catalytic agent to form a mixture, the liquid crystalmonomers having a mass percentage of about 42.2% to about 52.2% of atotal mass of the mixture, the silver complex having a mass percentageof about 43.1% to about 53.1% of the total mass of the mixture, theinitiator having a mass percentage of about 0.85% to about 1.35% of thetotal mass of the mixture, and the catalytic agent having a masspercentage of about 2.85% to about 4.35% of the total mass of themixture; adding a solvent into the mixture, the mixture and the solventbeing in a ratio from 3:17 to 1:3 by weight; and heating the mixture toundergo atom transfer radical polymerization.
 2. The method of claim 1,wherein the liquid crystal monomers are selected from a group consistingof 2,5-bis[(4methoxyphenyl)oxycarbonyl]styrene, 4-vinyl benzene andderivant thereof, methyl acrylate, hydroxyethyl acrylate, vinylacrylate, N,N-dimethylamino propenyl ketone, acrylonitrile, methylmethacrylate, butyl methacrylate, N,N-dimethylaminoethyl methacrylate,and tert-butyl methacrylate.
 3. The method of claim 1, wherein thesilver complex is selected from a group consisting of AgNO₃, Ag₂O,AgBP₄, and AgPF₆.
 4. The method of claim 1, wherein the initiator isselected from a group consisting of1,3,5-(2′-bromo-2-methylpropionato)benzene, α-bromine ethane, 2-ethylbromide, 2-bromine-2-methyl ethyl propionate, and 2-dibrominepropionitrile.
 5. The method of claim 1, wherein the catalytic agent iscopper bromide.
 6. The method of claim 1, wherein the catalytic agent iscopper bromide and sparteine.
 7. The method of claim 1, wherein thesolvent is selected from a group consisting of dimethyl sulfoxide,dimethylformamide, and N-methyl-2-pyrrolidone.